In recent years there has been an increased awareness that the underground storage and distribution systems of hazardous fluids, such as, hydrocarbon fuels and a diversity of chemicals, need to be improved to prevent any leaking product from these systems from escaping into the environment and potentially contaminating the underground drinking water. Both public health and fire safety regulatory bodies have imposed strict guidelines and regulations on such systems to insure public safety.
Leaking underground storage tanks and their associated underground piping systems became the focus of the Federal Environmental Protection Agency (EPA) to initiate federal and state legislation that would require an improved means of storage, distribution, leak detection and accounting of all stored fluids which are deemed to be hazardous. The EPA conducted studies which showed that underground piping failures were caused by poor installation practices, corrosion and structural failure were responsible for most of the leaks reported.
In response to this public awareness and concern, equipment specifiers and manufacturers have developed improved piping systems in recent years to provide a greater degree of protection for the environment. Most of these improved piping systems provide a second barrier of protection around the primary fluid supply piping, commonly referred to as "secondary containment".
In addition to the regulatory bodies mentioned above, facility owners and their insurance companies have become very concerned with the type of materials used and the design specifications of existing, new and proposed fuel storage, transmission and dispensing equipment. An important area of concern is the chemical compatibility of the materials used in the construction of both the primary and secondary containment systems. As a result, Underwriters Laboratories Inc. (UL), a nationally recognized and accepted independent testing laboratory, has already established and proposed new standards for both the primary and secondary containment underground storage, transmission and dispensing equipment. Acceptable materials for use in this application generally relate to the materials stability when exposed to conditions and chemicals found naturally in a subterranean environment and the exposure to the fuels and their chemical additives, as well as other chemicals being stored and dispensed. In addition, another area of concern is ability of a material to provide an acceptable containment barrier for the product to be stored. The product permeability rating of a material is generally accepted by regulators and UL as being more stringent for the primary storage vessel than the secondary containment vessel, which only provides a means of temporary storage of leaking product until detected and corrected.
For example, UL has established and proposed new standards which include acceptable permeability levels for the primary containment and secondary containment storage and dispensing systems. These standards require that a typical primary wall section should not be able to permeate more than 1% of its stored product weight over a period of 270 days, whereas, a typical secondary containment wall section should not be able to permeate more than 1% of its stored product over a period of 30 days. Keeping these standards in mind, UL listed products for storage of hazardous liquids and fuels must be constructed of the proper materials at the acceptable thickness to provide a satisfactory level of environmental protection and fire safety.
For purpose of this description, "underground piping systems" is defined as the means of transferring hazardous liquids from a buried underground storage "tank", by the tanks electrically powered dispensing "pump" to a generally metered dispensing unit or "dispenser", generally located above ground. An underground piping system which is secondarily contained by a larger diameter piping system is generally referred to as a "double-wall piping system". The primary distribution pipe which is contained is commonly referred to as the "supply pipe" and the larger outer secondary containment pipe is commonly referred to as the "containment pipe". Other secondary containment components, such as, surface access chambers, which are installed around the tanks pump and underneath a dispenser, are commonly referred to as "access sumps". These storage, transferring and dispensing systems, are typically found at service stations which market gasoline and diesel fuel.
Equipment manufacturers have in recent years introduced both patented and non-patented supply piping systems and/or secondary containment systems for these supply piping systems of various designs and material selections. The following double wall piping systems which are considered to be prior art of this invention, are disclosed as follows:
(1). A secondarily contained underground piping system which features a non-flexible fiberglass supply pipe system fully contained by a larger non-flexible fiberglass containment piping system. One such system also includes the feature of telescoping containment pipe, whereby two non-flexible containment pipes are offered, one with a slightly larger inside diameter than the outside diameter than the other. This permits larger pipe to be installed over the smaller pipe therefore exposing more of the supply pipe contained within both. The containment pipe and fittings are of a larger inside diameter than the outside diameter of the supply pipe and fittings contained within. The short bend radius containment fittings and couplings are of a clamshell design (two piece) to permit assembly of the the short bend radius supply fittings prior to assembly of the containment piping system. Both the supply and containment piping components are joined together by heat activated resins to insure a liquid tight joint. These systems are generally difficult to install due to the nature of their design and joining system. Both the supply and containment piping system are made of fiberglass which provides excellent chemical compatibility and impermeability.
(2). A secondarily contained underground piping system which features a non-flexible fiberglass or steel supply pipe fully contained by a combination of both a larger flexible and non-flexible polyethylene telescoping containment pipe. The telescoping containment pipe design that permits the complete inspection of the supply pipe line during assembly and integrity testing. This containment piping system includes a flexible containment pipe which is sufficiently flexible to go around and contain short bend radius supply elbow fittings. An oversized short bend radius containment tee fitting is provided for insertion, assembly and inspection of the smaller short bend radius supply tee fittings before the containment system is assembled. The containment components of this system are joined by means of metal fasteners and flexible seals. The flexible polyethylene containment pipe is not of sufficient wall thickness and density to offer the level of impermeability necessary to meet the UL standard. The non-flexible polyethylene containment pipe is of sufficient wall thickness and density to meet the UL standard. Both the contained fiberglass or steel supply pipe will meet the UL standard. Note: The metal fastener use to make a compression will not meet the UL standard for corrosion resistance.
(3). A secondarily contained underground piping system which features a non-flexible fiberglass or steel supply pipe fully contained by a larger non-flexible polyethylene telescoping containment pipe. The telescoping containment pipe design permits the complete inspection of the supply pipe line during assembly and integrity testing. This containment piping system includes short bend radius clamshell (split) containment fittings that permits assembly and inspection of the smaller short bend radius supply fittings before the clamshell containment are assembled over them. The containment components of these systems are generally joined by means of metal fasteners and flexible seals. Both the non-flexible polyethylene containment pipe and contained fiberglass or steel pipe will meet the UL standard.
(4). A secondarily contained underground piping system which features a fiberglass or steel non-flexible supply pipe partially contained by a flexible membrane piping trench liner. This type of secondary containment system provides a single containment system for a multitude of supply pipe lines contained within. These piping trench lining systems are generally custom fabricated at the jobsite and are typically joined by mechanical means using metal fasteners and flexible seals. These piping containment systems are often difficult to install, damage prone, directionally limiting and do not provide a full measure of secondary containment. The material composition of these liners do not offer sufficient wall thickness or density to meet the UL standards. Note: The metal fastener use to make a compression will not meet the UL standard for corrosion resistance.
(5). A secondarily contained underground piping system which features a fiberglass or steel non-flexible supply pipe partially contained by a non-flexible fiberglass trench liner. This type of secondary containment system provides a single containment system for a multitude of supply pipe lines contained within. These piping trench lining systems are generally factory fabricated and shipped in large sections for assembly at the jobsite and are joined by heat activated resins in combination with glass fiber reinforcement. The material composition of these liners is sufficient to meet the UL standards.
(6). A secondarily contained underground piping system which features a flexible nylon composite supply pipe fully contained by a larger flexible polyethylene containment pipe. The flexible supply pipe has internal corrugations for added flexibility and requires metallic couplings installed on each end of a pipe section for attachment to a metallic short bend radius tee or elbow supply fitting. The flexible containment pipe is a thin wall corrugated tube which provides added flexibility and structural strength. This type of secondarily contained piping system requires the use of access sumps which are interconnected by continuous runs of both flexible supply and containment pipe sections. These access sumps provide a means of containment for the metallic supply couplings and fittings as well as the containment pipe connections. Both the supply and containment components are joined by mechanical means using rubber gaskets and washers for seals. The material composition of the flexible supply pipe will not the UL standard for primary containment of alcohol and alcohol blended fuels. The material composition of the the flexible containment pipe is not of sufficient thickness or density to meet the UL standards for secondary containment.
(7). A secondarily contained underground piping system which features a flexible rubber composite supply pipe fully contained by a larger flexible polyurethane composite containment pipe. The flexible supply pipe is made a rubber elastomeric material for flexibility and requires metallic couplings installed on each end of a pipe section for attachment to a metallic short bend radius tee or elbow supply fitting. The flexible containment pipe is a thick wall tube which provides structural strength but limited flexibility. This type of secondarily contained piping system requires the use of access sumps which are interconnected by continuous runs of both flexible supply and containment pipe sections. These access sumps provide a means of containment for the metallic supply couplings and various adapters. Both the supply and containment components are joined by mechanical means using rubber gaskets and washers for seals. The material composition of the flexible supply pipe will not meet the UL standard for primary containment.
In addition to the secondarily contained underground piping systems, described above, a number of fiberglass and steel tank manufactures, as well as piping and specialty containment manufacturers have introduced access sumps to the market. These access sumps originated from a product called a backfill retainer which was simply a round cylinder, open at the top and bottom, which was installed around the tanks pump and under the street access manhole to keep the backfill materials away from the pump and various plumbing connections. Often a short section of corrugated metallic culvert was used for this purpose. In the early-1980's, fiberglass tank manufacturers began to offer an improved backfill retainer, called a riser and riser extension which connected to the tank and was made made of non-corrodible fiberglass material. Steel tank manufactures soon followed with there own version of a riser made of coated steel. When the industry became aware that underground tanks and piping needed to be secondarily contained, they also turned their attention to the tanks pump and miscellaneous plumbing connections. Soon thereafter, pump access chambers appeared on the market as a means of secondarily containing the tanks pump and associated plumbing connections. With the introduction of these watertight chambers it was quickly recognized that they could also be used as a fluid collection and detection sump for the attached secondarily contained piping systems described above. Because these chambers were located at the low end of a sloped secondarily contained piping line, they were logical choice for the collection point for any leaking product which was contained inside the containment pipe. From this point on they were considered to be a multi-purpose chamber and were commonly referred to as pump access sumps.
As the full scope of secondary containment requirements began to unfold, attention was turned to the causes of product leaks from within and under the above ground dispenser such as leaking plumbing joints and spillage from required fuel filter changes. The solution seemed to be a shallow collection sump installed directly under the dispenser. The first dispenser collection sumps were shallow and were commonly referred to as dispenser pans. Soon thereafter it was recognized that a deeper dispenser pan was required to contain the entire metallic flexible connector which was installed directly under the dispenser. These deeper dispenser pans became commonly known dispenser access sumps. These dispenser sumps were not developed as an extension of the secondarily contained piping systems but rather were adapted to accommodate these piping systems.
Manufacturers of these access sumps began to offer a means of attaching and sealing various pipe and conduit entries into these access sumps. One approach was to pre-install cuffed openings at various locations in the side wall of the access sump. Manufactures of fiberglass access sumps laminated in fiberglass couplings into the side wall of the access sump for attachment of fiberglass pipe by means of fiberglass lamination or by means of a common rubber reducer seal used in the plumbing industry. Manufacturers of steel access sumps provided welded on couplings which served a similar purpose. Later, as molded polyethylene access sumps began to be introduced to the market, a variety of pipe entry seals were employed to accommodate all the available types of piping systems. Listed in order of their introduction are descriptions of these pipe and conduit sealing means. (a) A plastic molded cuff which was installed over an opening in the side wall which was attached by means of plastic welding in the field. This plastic cuff, was similar in design and purpose to those provided with the fiberglass and steel access sumps for sealing pipe entries. (b) A conventional plastic bulkhead fitting was used for conduit entries. (c) A commercially available rubber grommet was offered to replace the plastic cuffs and bulkhead fittings for sealing both pipe and conduit entries. The rubber grommet was installed into an opening in the side wall of the access sump. (d) A rubber flanged boot was offered as a solution to the leaking rubber grommets. This rubber boot is inserted inside an opening in the side wall of the access sump and mechanically attached to the side wall by means of bolt fasteners. The significant advantage of this type of sealing device was that it provided a watertight seal for both conduit and pipe entries that could be installed in any desired location in the side wall of the access sump. These various sealing devices evolved over time to accommodate most of the secondarily contained piping systems described above. Only two types of conduit sealing means were developed for a specific application which are described as follows: (a) A plastic internal facing cuff was molded in at specific locations into the side wall of the polyethylene access sumps to seal flexible corrugated polyethylene containment pipe entries. These sumps were a required component of a secondarily contained underground piping system which features a flexible nylon composite supply pipe fully contained by a larger flexible polyethylene containment pipe. (b) A plastic external facing cuff was integrally molded at specific locations into the side wall of the polyethylene access sumps to seal thick walled smooth flexible containment pipe entries. These sumps were required components of a secondarily contained underground piping system which features a flexible rubber composite supply pipe fully contained by a larger flexible polyurethane composite containment pipe.
The introduction of continuous flexible supply pipe, a number of years ago, was a means of reducing the amount of connection joints in the supply pipe compared to the commonly used steel and fiberglass non-flexible supply piping systems. The first flexible supply pipe which was introduced was a non-contained thin walled flexible copper tubing which was directionally bent to accommodate the routing required to connect the tanks pump to the various dispenser. The second flexible supply piping system was introduced in Europe, which was a direct burial or non-contained flexible polyethylene tubing which had thick wall and offered only a limited amount of flexibility. Both of these flexible supply piping systems did not require the use of access sumps. The third flexible supply piping was introduced several years ago and was secondarily contained inside a flexible containment pipe and did require the use of access sumps. Two versions of this type flexible piping system were introduced approximately at the same time and are briefly described above.
Some notable advantages of these flexible double wall piping systems include considerably fewer piping joints than conventional double wall piping systems and also provide the unique feature of removing the supply pipe, in the event of a problem, without the need for excavation. These systems feature continuous lengths of both flexible supply pipe and flexible containment pipe which are made available in rolls of very long lengths. From these long lengths, pipe sections may be custom cut to length for installation between two or more surface access sumps. This feature eliminates the need for any directional fittings in the flexible containment pipe line, thus eliminating the need of any piping joints between the interconnected access sumps. The flexible primary piping does require the use of directional fittings but these fittings are located within the surface access sumps where they are surface accessible for inspection and maintenance. This piping design permits complete access to and observation of all the primary and secondary piping joints from the ground surface without the need for excavation.
Some notable disadvantages of both of these flexible double wall piping systems are as follows: (a) Thin walled corrugated flexible containment pipe is easy to damage and difficult to repair. The inner corrugations restrict fluid migration from the source of the leak to the collection sump. The thin polyethylene material will not meet the UL standard for secondary containment. (b) Thick walled non-corrugated flexible containment pipe requires the use of a soft elastomeric material in order to achieve limited flexibility. It is questionable as to whether or not this material will meet the UL standard for secondary containment. (c) Inner corrugated flexible supply pipe provides good flexibility but poor hydraulic flow efficiency and a low maximum operating pressure. The internal corrugations cause to pipe to be pressure expandable, which can produce faulty readings for in-line leak detection devices and make it difficult to connect internally expanded coupling devices, which could result in a leak. (d) Thick walled flexible rubber supply pipe is heavy and has a highly resistive outer surface which makes it difficult to install into the flexible containment pipe. Rubber material is an unsatisfactory material to use as a supply pipe and will not likely meet the UL standard for primary containment.
All of the secondarily contained piping systems and access sumps discussed above have developed over a relatively short period of time in response to the continuously changing environmental and safety regulations. The design criteria used by various manufacturers for the development of their products was dependent on what the considered to be important and what they felt they had the capability to produce. As a result none of the assembled systems described above is the absolute solution to a secondarily contained underground piping system. Certain component parts and design concepts of these discussed containment systems provide only partial solutions in developing an ideal piping containment system which meets the most important design criteria.